The present invention relates to devices for attachment to a pipe or vessel through which a fluid flows for monitoring the accumulation of a substance of substances on the interior surface of the pipe or vessel.
In, for example, the semi-conductor industry a low pressure chemical vapor deposition process is used to apply a deposition to wafers or substrates in a vacuum furnace. In such a process, for example, dichlorosilane and ammonia pass through the vacuum furnace which has been loaded with wafers in order to deposit silicon nitride on the wafers, leaving ammonia, hydrogen chloride, excess dichlorosilane and hydrogen as waste gases. The waste gases exit via a fore-line, vacuum pump and exhaust line and ammonium chloride and other substances can be formed and deposited as a solid on the inside surface particularly of the exhaust pipe. This tendency for the ammonium chloride to leave an accumulative deposit on the inside surface of the exhaust pipe in particular has required the regular manual inspection of the exhaust pipe to ensure that the exhaust pipe doesn't become excessively blocked and thereby prevent the flow therethrough of the waste gas and/or put an unnecessary mechanical strain on the vacuum pump.
It has been known to place in the interior of the exhaust pipe a sensor for monitoring the build up of deposits such as ammonium chloride on the inside surface of the exhaust pipe. However, it has been found that by placing a sensor on the inside of the pipe only encourages deposits not only on the inside surface of the pipe but also on the sensor itself. Furthermore the actual presence of the sensor physically restricts the flow of waste gases through the exhaust pipe. It is an aim of the present invention to provide a non-intrusive device for attachment to a pipe or a vessel through which a fluid flows for monitoring the accumulation of deposits on the interior surface of the pipe or vessel.